Control apparatus for vehicle AC generator

ABSTRACT

An arrangement including an AC generator  1  whose output voltage is regulated with a control quantity for a field current flowing through a field coil  102  of the AC generator, a switching element 308 for performing on/off-control of the field current flowing through the field coil  102  with a predetermined duty ratio, a voltage detecting means  305  for detecting an output voltage of the AC generator  1,  and a gradually increasing control means  4 A for increasing gradually a conducting rate by increasing gradually the duty ratio in dependence on the detected output voltage, and a rotation speed detecting means  13  for detecting a rotation speed of the generator  1,  wherein the gradually increasing control means  4 A is designed to increase the gradually increasing rate of the duty ratio in conformance with increasing of the rotation speed detected by the rotation speed detecting means  13.

TECHNICAL FIELD

The present invention relates to a control apparatus for avehicle-onboard AC generator.

BACKGROUND ART

FIG. 3 is a circuit diagram showing a structure of a control apparatusfor a conventional vehicle AC generator which is disclosed, for example,in Japanese Utility Model Registration Application No. 34900, 1989.

Operation of the conventional apparatus will be described by referenceto this circuit diagram.

When a key switch 8 is closed upon starting of an engine, a base currentflows to a power transistor 308 from a battery 7 by way of the keyswitch 8, a reverse-current blocking diode 11, a resistor 12 for initialexcitation and a base resistor 309 of the power transistor 308, as aresult of which the power transistor 308 is turned on, i.e., turned to aconducting state.

When the power transistor 308 is turned on, a field current flows to afield coil 102 from the battery 7 by way of the key switch 8, thereverse-current blocking diode 11, the resistor 12 for initialexcitation, the field coil 102 and the power transistor 308, whereby anelectric generator 1 is set to the state capable of generatingelectricity.

When engine operation is started, the generator 1 is rotationallydriven, whereby generation of electricity is started. In this state, adivided voltage obtained by dividing a generated voltage of thegenerator 1 with voltage dividing resistors 301 and 302 is compared witha reference voltage derived from voltage division of a constant voltagesupplied from a constant-voltage power source A with voltage dividingresistors 303 and 304 by means of a comparator 305 of a voltageregulator 3. When the divided voltage resulting from the division of thevoltage generated by the generator 1 is equal to or lower than thepreset reference voltage value resulting from the voltage division ofthe voltage of the constant-voltage power source A, the comparator 305assumes a conducting or on-state from a non-conducting or off-state,which results in that a transistor 306 is turned off from the conductingstate or on-state.

When the power transistor 308 is turned on, then the field current tendsto flow through the field coil 102. However, because the comparator 305is in the conducting state, the voltage smoothed by a smoothing circuit4 is discharged to a discharging resistor 405 from a capacitor 404.

In this conjunction, it is noted that the discharging time constantdetermined by the capacitor 404 and the discharging resistor 405 islarge. Consequently, the output of a comparator 601 assumes on- andoff-state periodically at a predetermined interval until it is detectedthat the generated voltage of the generator 1 reaches a predeterminedvalue through comparison of a triangular waveform voltage outputted froma triangular waveform generator 5 with the discharge voltage of thesmoothing circuit 4.

As a result of this, a transistor 602 is turned on and off in responseto the output of the comparator 601, whereby the power transistor 308 isturned on and off with a predetermined duty ratio to thereby control thefield current flowing through the field coil 102 such that generation ofthe output current of the generator 1 is retarded.

When the output current of the generator 1 has reached a current levelequivalent to a load current of a vehicle electric load 9 with thegenerated voltage of the generator 1 reaching a predetermined value, theoutput of the comparator 601 assumes on/off levels with such a dutyratio to produce the on/off control of the field current demanded forthe output current of the generator 1.

The transistor 602 is turned on/off in response to the output of thecomparator 601 to thereby control the power transistor 308 and hence thefield current flowing through the field coil 102, as a result of whichthe generated voltage of the generator 1 is regulated to thepredetermined value.

As is apparent from the above, in the case of the conventionalapparatus, the resistance value of the charging resistor 402 for thecapacitor 404 constituting a part of the smoothing circuit 4 is selectedto be small while that of the discharging resistor 405 is selectedlarge. Thus, the value of the time constant for electric charging is setshort or small (e.g. not greater than 0.5 sec.), whereas the timeconstant for electric discharge is set long or large (e.g. not smallerthan 0.5 sec.), whereby such operation is ordinarily realized that theoutput of the comparator 601 becomes substantially equivalent to theoutput of the comparator 305 which constitutes a part of the voltagedetecting circuit.

FIG. 4 shows changes in the generator output voltage waveform in thestate where the vehicle-onboard electric load (e.g. headlight) is turnedon in response to the turning-on or closing of a switch 10 and changesin the conducting rate of the power transistor 308 in consideration ofthe discharge characteristic.

In the conventional apparatus such as described above, the charging timeconstant of the smoothing circuit is set short while the dischargingtime constant is set long, wherein each of the time constants mentionedabove is always set to a fixed value. Consequently, the ration ofconduction of the power transistor 308 increases progressively orgradually in dependence on the magnitude of the discharging timeconstant which is effective when the electric load 9 is turned on andfinally reduces a predetermined conducting rate after lapse of apredetermined time. Thus, the generator output voltage falls oncetemporarily to ΔV1 upon turning-on electric energizing of the electricload 9 and thereafter gradually increases in conformance with theconducting rate of the power transistor 308.

The conventional apparatus is certainly effective for minimizing adecrease of the engine rotation number (rpm) by gradually increasing theoutput power of the generator when the engine, by which the generator isdriven, is in the idling state. However, because the operation ofgradually increasing the generator output is effective equally in ahigh-speed rotation state where the engine output allows a margin, theoutput voltage of the generator always falls every time the electricload is turned on, which in turn brings about variation in the outputstates of the loads already set to the on-state such as variation inluminance of lamps installed on instrumentation panels, room lamps, etc.which is of course uncomfortable for the driver, giving rise to aproblem.

DISCLOSURE OF THE INVENTION

The present invention has been made with a view to solving the problemas mentioned above, and thus as object of the present invention is toprovide a control apparatus for a vehicle AC generator which is capableof lengthening a time period during which the field duty (i.e., dutyratio of the field current) gradually increases, to thereby minimize areduction of the engine rotation number upon turning-on of an electricload, while shortening a time period during which the field duty (i.e.,duty ratio of the field current) is gradually increased, to therebyminimize reduction of the generator output voltage when the electricload is turned on.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a structure of a control apparatus for avehicle-onboard AC generator according to a first implementation mode ofthe present invention.

FIGS. 2(a) to 2(c) are characteristic diagrams for illustratingrelations between generator output voltage and conducting rate of apower transistor in the apparatus according to the first implementationmode of the invention.

FIG. 3 is a view showing a structure of a conventional control apparatusfor a vehicle-onboard AC generator.

FIG. 4 is a characteristic diagram for illustrating relations betweengenerator output voltage and conducting rate of a power transistor inthe conventional apparatus.

BEST IMPLEMENTATION MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a diagram showing a structure of a control apparatus for avehicle-onboard AC generator according to a first implementation mode ofthe invention concerned. In the figure, same reference numerals as thoseused in FIG. 3 denote same or equivalent parts. Shown in FIG. 2 at (a)is a characteristic diagram for illustrating a relation between agenerator output voltage and a conducting rate of a power transistor inan idling operation state of an engine, while shown in the same figureat (b) is a characteristic diagram for illustrating a relation between agenerator output voltage and a conducting rate of the power transistorin a moderate-speed rotation state of the engine, and shown in the samefigure at (c) is a characteristic diagram for illustrating a relationbetween an output voltage of the generator and a conducting rate of thepower transistor in a high-speed rotation state of the engine.

Referring to FIG. 1, reference numeral 13 denotes a F-V converter whichconstitutes a rotation speed detecting means. This F-V converter 13 isdesigned for detecting a rotation frequency of the generator 1 on thebasis of a frequency of an AC voltage induced in the armature coil 101to thereby convert the rotation frequency (F) into a DC voltage (V). TheDC voltage (V) resulting from the conversion assumes a large value inproportion to the rotation frequency (F).

Reference numeral 407 denotes an NPN transistor which constitutes a partof a constant-current circuit. This NPN transistor 407 has an emitterelectrode connected to the ground of the apparatus, while collector andbase electrodes thereof are connected in common to an output voltageterminal of the F-V converter 13 via a current limiting resistor 408.

Further, in a smoothing circuit 4A of the apparatus according to theinstant implementation mode of the invention, a transistor 406 isemployed in place of the discharging resistor 405, wherein the collectorand the emitter of the transistor 406 are connected in parallel to thecapacitor 404 with the base of the transistor 406 being connected tothat of the NPN transistor 407.

Next, operation of the apparatus according to the instant implementationmode will be described by reference to FIG. 1 and FIG. 2.

At first, assuming that the electric load 9 is electrically energized byturning on the switch 10 when the engine rotation number is low as inthe case of idling of the engine, the conducting rate of the powertransistor is so regulated as to minimize reduction of the enginerotation number by lengthening the time period during which the fieldduty is gradually increased.

To this end, the F-V converter 13 serves for detecting the rotationfrequency of the generator 1 in the idling state of the engine, tothereby convert the rotation frequency into a DC voltage which is thenapplied to the base of the transistor 407 constituting a part of theconstant-current circuit by way of the current limiting resistor 408.

The NPN transistor 407 allows a constant current determined by thecurrent limiting resistor 408 and the voltage value resulting from theconversion to flow to the base of the transistor 406 which constitutes apart of the smoothing circuit 4A.

When the current flows to the base of the transistor 406, electriccharges stored in the capacitor 404 are discharged as a collectorcurrent, as a result of which a discharge voltage is applied to aninversion input terminal of the comparator 601. In that case, becausethe collector current is small and thus the discharge voltage rises onlygently, the discharging time constant may be regarded to be large.

The transistor 602 is periodically turned on and off with the ON/OFFduty ratio being gradually increased until it is detected that theoutput voltage of the generator 1 has reached a predetermined valuethrough comparison of the discharge voltage of the smoothing circuit 4and the triangular waveform voltage generated by the triangular waveformgenerator 5.

As a result of this, the power transistor 308 is also turned on and offin conformance with the turn-on/off operation of the transistor 602. Thefield current flowing through the field coil 102 thus undergoes on/offcontrol by means of the power transistor 308, whereby the output voltageof the generator 1 is caused to increase or rise gradually and gently upto a predetermined value in conformance with the dischargecharacteristic determined by the discharging time constant, as a resultof which decreasing of the engine rotation can be reduced.

On the other hand, upon power-on of the electric load 9 at a time pointat which the engine rotation speed has reached the moderate speed afterlapse of a predetermined time from starting of the engine, the convertedvoltage outputted from the F-V converter 13 and having higher level thanthat in the idling operation state is inputted to the constant-currentcircuit, whereby the base current at the moderate-speed operation stateof the engine is fed to the base of the transistor 406 as the basecurrent, as illustrated in the same figure at (b).

Due to the base current of the transistor 406 which is larger than thatin the idling operation state, the electric charges stored in thecapacitor 404 are discharged speedily. Thus, the rate of change of thedischarge voltage as a function of time assumes a greater value thanthat in the idling operation state. Thus, the discharging time constantmay be regarded smaller than that in the idling operation state.

The transistor 602 is periodically turned on and off with the ON/OFFduty ratio being gradually increased during a shorter time period thanthat in the idling operation state until it is detected that the outputvoltage of the generator 1 has reached the predetermined value throughcomparison of the discharge voltage of the smoothing circuit 4 and thetriangular waveform voltage generated by the triangular waveformgenerator 5.

As a result of this, the power transistor 308 is also turned on and offin conformance with the turn-on/off operation of the transistor 602. Thefield current flowing through the field coil 102 thus undergoes on/offcontrol by the power transistor 308, whereby the output voltage of thegenerator 1 is caused to increase or rise gradually and gently up to thepredetermined value in accordance with the discharge characteristicdetermined by the discharging time constant, as a result of whichdecreasing of the output voltage of the generator can be reduced.

On the other hand, as shown in the same figure at (c), upon power-on ofthe electric load 9 at a time point at which the engine rotation speedhas reached a high speed after lapse of a predetermined time from thestart of the engine operation, the converted voltage outputted from theF-V converter 13 and having higher level than that in the moderate speedoperation state is inputted to the constant-current circuit, whereby theconstant current in the high-speed operation state of the engine is fedto the base of the transistor 406 as the base current.

Because the constant current which is larger than that in themoderate-speed operation state flows to the base of the transistor 406,the electric charges stored in the capacitor 404 are dischargedspeedily. Thus, the rate of change of the discharge voltage as afunction of time lapse assumes a greater value than that in themoderate-speed operation state of the engine. Thus, the discharging timeconstant may be regarded smaller than that in the moderate-speedoperation state.

The transistor 602 is periodically turned on and off with the ON/OFFduty ratio being rapidly increased until it is detected that the outputvoltage of the generator 1 has reached the predetermined value throughcomparison of the discharge voltage of the smoothing circuit 4 and thetriangular waveform voltage generated by the triangular waveformgenerator 5.

As a result of this, the power transistor 308 is also turned on and offwith the duty ratio which conforms with the on/off operation of thetransistor 602. The field current flowing through the field coil 102thus undergoes on/off control by the power transistor 308, whereby theoutput voltage of the generator 1 is caused to increase or rise rapidlyup to the predetermined value in accordance with the dischargecharacteristic determined by the discharging time constant, as a resultof which decreasing or fall of the generator output voltage can bereduced when compared with that in the moderate-speed rotation state ofthe engine.

Industrial Applicability

According to the present invention, the rate at which the generatoroutput voltage gradually increases conforms to an increased rotationspeed of the generator, which in turn depends on the engine rotationnumber. During the low speed operation state of the engine, the timeperiod during which the generator output voltage gradually increases islengthened to thereby minimize reduction of the engine rotation, whereasin the high-speed operation state of the engine, the time period duringwhich the generator output voltage gradually increases in shortened tothereby minimize lowering of the generator output voltage.

What is claimed is:
 1. A control apparatus for a vehicle AC generatorcomprising: an AC generator having an output voltage regulated bycontrolling a quantity of a field current flowing through a field coilof said AC generator; a voltage regulator having a transistor connectedto said field coil for performing on/off-control of the field currentflowing through said field coil with a predetermined duty ratio; afrequency-voltage converter connected to an armature coil of said ACgenerator for detecting a rotation frequency of said AC generator andconverting the rotation frequency to a voltage; a constant currentcircuit having a transistor with base and collector electrodes whichreceive the voltage output from said frequency-voltage converter; and asmoothing circuit having a transistor operative to discharge a voltage,wherein the collector and emitter electrodes of the transistor connectedin parallel to a capacitor and a base electrode connected to the baseand collector electrodes of the constant current source, wherein adischarging time constant of said smoothing circuit decreases as therotation speed detected by said frequency-voltage converter increases,and wherein the output voltage of said AC generator increases graduallyup to a predetermined value in conformance with the dischargecharacteristics of the discharging time constant.
 2. A control apparatusfor a vehicle AC generator comprising: an AC generator whose outputvoltage is regulated by controlling a quantity of a field currentflowing through a field coil of the AC generator; a switching elementfor performing on/off-control of the field current flowing through saidfield coil with a predetermined duty ratio; voltage detecting means fordetecting an output voltage of said AC generator; rotation speeddetecting means for detecting a rotation speed of said generator; andcontrol means for gradually increasing a conducting rate of saidswitching element by gradually increasing said duty ratio in dependenceon the detected output voltage, said control means further comprising: asmoothing circuit which outputs a discharge voltage, and is operative tosmooth the detected voltage of the voltage detecting means and todecrease a discharging time constant as the rotation speed detected bythe rotation speed detecting means increases; triangular waveformgenerating means for generating a triangular waveform voltage; andcomparing means for comparing said discharge voltage of said smoothingcircuit with said triangular waveform voltage, to thereby output anon/off control signal for the switching element, wherein said controlmeans is operative to gradually increase said duty ratio in conformancewith an increase in the rotation speed detected by said rotation speeddetecting means.
 3. A control apparatus for a vehicle AC generator asset forth in claim 2, characterized in that the rotation speed detectingmeans comprises a frequency-voltage converter for converting arotational frequency into a voltage indicative of the rotation speed. 4.A control apparatus for a vehicle AC generator comprising: an ACgenerator whose output voltage is regulated by controlling a quantity ofa field current flowing through a field coil of the AC generator; aswitching element for performing on/off-control of the field currentflowing through said field coil with a predetermined duty ratio; voltagedetecting means for detecting an output voltage of said AC generator;control means for gradually increasing a conducting rate of saidswitching element by gradually increasing said duty ratio in dependenceon the detected output voltage; rotation speed detecting means fordetecting a rotation speed of said generator, wherein the control meansfurther comprises: a smoothing circuit operative to smooth the detectedvoltage of the voltage detecting means and to decrease a dischargingtime constant as the rotation speed detected by the rotation speeddetecting means increases; triangular waveform generating means forgenerating a triangular waveform voltage; and comparing means forcomparing a discharge voltage of said smoothing circuit with saidtriangular waveform voltage, to thereby output an on/off control signalfor the switching element, wherein said control means is operative togradually increase said duty ratio in conformance with an increase inthe rotation speed detected by said rotation speed detecting means; andwherein the smoothing circuit further comprises: a constant-currentcircuit with a current level that increases with an increase in therotation speed of said generator; and a smoothing capacitor, wherein arate at which voltage is discharged from the smoothing capacitorincreases as said current value increases.
 5. A control apparatus for avehicle AC generator as set forth in claim 4, characterized in that thecharge or discharging time constant of the smoothing circuit is not lessthan 0.5 second.